1. Technical Field
The present disclosure relates in general to signal processing and in particular to signal processing utilizing a programmable multirate filter.
2. Description of the Related Art
There has been a dramatic increase in multi-mode use in cellular radio devices, or cell phones as they are conventionally known. This fact coupled with the availability of both multiple bandwidth options for a given radio access technology (RAT) and RAT combinations from 3RD Generation Partnership Project (3GPP) & 3GPP2 standards has increased the importance of sample rate conversion. This increased importance is especially pronounced for cellular modems.
There are multiple standards and technologies supported by common RF components. In order to reduce power and area requirements on the chips, it has become increasingly desirable to utilize common baseband sampling rate to address multiple technologies. This implementation can involve the use of multirate filters. To achieve accurate timing, delay through multirate filters must be deterministic. However, providing deterministic delays can be difficult due to crossing clock domains and unknown clock phase relationships. Also, it is not practical to use lowest common sampling frequency to hit exact timing corrections. For example, achieving ¼ chip adjustments for cell division multiple access (CDMA) using long term evolution (LTE) 1.92 MHz sampling rate would require upsampling and filtering of data at 100× (122.88 MHz). Also, uplink timing synchronization is critical for uplink performance. There is currently no efficient method to sample signals that properly accounts for a diverse set of signal frequencies and phase relationships and which can also account for jitters inherent in the input and/or output clocks of a multirate filter.